This invention relates generally to eddy current testing methods and apparatus, and more particularly to an eddy current type of method and apparatus for measuring hole diameter and determining the eccentricity of the hole.
Hole inspection systems utilizing such devices as dowel pins and hole gauges, are generally known. Also known are capacitance type hole probe systems as well as systems using eddy current probes including surface probes and hole probes. A hole probe utilized in an eddy current inspection system is relatively close to the same diameter as the hole being inspected, but must be small enough to fit into the hole without making any contact therewith.
In an eddy current probe, eddy currents are produced in an electrically conductive test piece by a coil through which an alternating current flows, and as a result of the eddy currents produced, impedance of the coil and the voltage applied to the coil are changed and thus measurement of a particular characteristic of the hole is determined by a measured change in the impedance of the sensor coil.